A Mossberg shotgun comes out of the box with “corncob” style plastic forearm that is completely functional and in a way minimalistic. It can get a little slick when wet, but not terribly so. About as bog standard as it gets.
The military decided to replace this forend with a tri-rail. A unit made by ERGO. https://www.ergogrips.net/
I gotta say I was wrong. In the past I’ve said that I didn’t get the point of railed handguards on a shotgun. Now I’ve never said anything bad about ERGO, but I never really was impressed with their grips. To me their grips felt too soft and the wrong angle and shapes. I was a little leery picking up an ERGO rail for my shotgun. I had a feeling that ERGO was kinda like TAPCO.
It is nice to say I was wrong about ERGO, their rail for the Mossberg is very nicely made.
First things first. Mossberg has two different lengths of action tube. Because of this, ERGO offers two different lengths of their forend. (ERGO now also offers a MLOK forend, might be a better choice for the average person should they want one) These military shotguns use the longer rail. There is an aftermarket threaded end cap that will allow the shorter tubes to accept the longer forend. That would be an excellent option for people who have the shorter tube who want to use a full length forend.
Another note, there are a couple versions of this rail. There is a commercial version with a relieved, not true M1913 rail. Then there is a bulk packed version with a proper M1913 picatinny rail.
This common photo of a M500A2 MEK shotgun shows the commercial rail, as you can see the notch milled down the center of the rail.
I bought a bulked packed rail from Pro Patria. ERGO part number 4865(BULK). The commercial version is part number 4865. MSRP is $96. I had a hard time finding it cheaper, so I am very grateful for the deal Pro Patria gave me of the rail and used barrel.
There is a threaded cap holding on the handguard on a Mossberg action tube. I found a sheet of metal that fit the notched and unscrewed the cap.
I’ve read horror stories of people taking off the plastic corn cob grip. People reporting they had to cut it off, or use an arbor press. Others make tools to take it off. I was able to hold the plastic and press the tube against a table top and it slipped right off. I used this oppertunity to coat the action tube with a thick layer of oil, and slid on the ERGO rail, and reinstalled the end cap with some Vibra-tite. Quick and easy.
Only complaint I would have with the install is that there is a fair bit of rotational tolerance, so I had to try and center the rail while I tightened the end cap. The end cap is the only thing keeping the rail from rotation a bit on the action tube. I think using a forward grip would easily provide enough torque to rotate the rail some on the action tube.
ERGO includes 3 ladder style rail covers with their rail that completely covers all the rail. I decided I wanted to try shooting this gun with the rail uncovered to see how it felt.
Here is where ERGO really surprised me.
Many cheap rail, and some expensive ones (like on the FN SCAR I got to use, and my Geissele rail) have sharp edges on them. Those are not too dissimilar to the “cheese grater” disparaging insult for rails systems.
This ERGO rail is perfectly deburred so that it feels just fine to use. It provides a much grippier surface than the plastic corncob forend. Shooting buckshot and holding the bare rail was not unpleasant. I had expected it to be painful. But the rail surfaces does grip your hand solidly during recoil. So I’m going to throw those rail covers on it.
There is a lot of wobble in a Mossberg action tube. The gun is designed with this leeway to allow for debris and still function. This means that this rail is completely unsuitable for any sort of aiming device.
So, why would the military want a railed forend?
Simple answer, to mount a light.
Unfortunately breaching is not often done in a bright well lit area. Military rails and room clearing often happen at night, or in dark indoor areas. It is critical for speed and efficiency that the breacher make their shots count. When they shoot to breach, it lets everyone know that we are here.
Why not a forend with an integrated light? Apparently the military looked at that option. Robert Clements, who developed this system, was able to get Insight to make a integrated light forend for the Mossberg.
Remington has an interesting solution. On the 870MCS, there are slots on each side of the handguard to install a little keyfob light.
The military isn’t looking for some super bright high lumen alternative to the sun. They want a low intensity light that provides some discrete illumination for the breacher. Tools like the old SOPMOD Low Intensity Tactical Illuminator (LITE).
This railed forend allows for mounting a low intensity light for breaching. Or any other standard weapon light when the shotgun is used as a primary weapon system. That is why the M500A2 MEK has a tri-rail